Optical Coherence Tomography (OCT) is a non-invasive, and often non-contact, imaging technique. Light with a defined coherence length is radiated on a sample that reflects or re-emits light at different depths of penetration, which encodes information in the phase of the light. The light from the sample is superimposed with coherent light of a reference branch.
Classical OCT systems used a movable mirror in a mechanical reference branch for a variable optical length of the reference branch. Modern OCT systems use Fourier Domain OCT (FD-OCT). The performance of an OCT system may be characterized by its axial resolution and/or its axial scanning depth.
In some of the existing OCT systems, the axial resolution or the axial scanning depth may be limited by features of the OCT system. By way of example, an OCT system using Spectral Domain OCT (SD-OCT, which is one case of FD-OCT) may have an axial scanning depth limited by the spectral resolution of a spectrometer. As another example, an OCT system using Swept Source OCT (SS-OCT, which is another case of FD-OCT) may have an axial scanning depth limited mainly by the instantaneous linewidth δλ of the swept source. Further, an OCT system using FD-OCT may have an axial resolution that cannot be adjusted independently of its axial scanning depth. For example, the scanning depth Δzmax may be proportional to the axial resolution δzmin for a given spectral or temporal resolution of the detector. Moreover, an SS-OCT system may have a lower axial resolution, because its swept source of light is tunable over an overall spectral bandwidth Δλ (also referred to as tuning range) that is narrower than a complete bandwidth Δλ of a light source usable for SD-OCT without tuning of the light source.